Analysis of pinning in NdBa2Cu3O7-δ superconductors

Current densities j(s) and volume pinning forces F-p are obtained in a wide temperature (5 less than or equal to T less than or equal to 92 K) and field range (0 less than or equal to mu(0)H(a)less than or equal to 9 T) on different NdBa2Cu3O7-delta samples. Above 60 K a good scaling of the volume pinning force F-p versus the reduced field h=H,IH,, can be established. The scaled pinning curves are compared to several theoretical predictions. Experimental evidence for strong pinning at extended superconducting defects (interaction volume V-pin similar to-xi(2)d) is given. These defects are ascribed to spatial composition fluctuations found in light rare-earth superconductors, providing a scatter of the transition temperature T,. Such a pinning mechanism is especially important for applications of high-T-c superconductors operating at T = 77 K.